This invention relates to a vertical cavity surface emitting laser ("VCSEL") and, more particularly, to a spatial absorptive and phase shift filter semiconductor layer to reduce modal reflectivity for the higher order modes in a VCSEL.
Vertical cavity surface emitting lasers are very desirable light sources for high speed laser printing, optical fiber communications and other applications. VCSELs have several advantages over edge emitting lasers including an emitted beam with a small angular divergence, a circular, anastigmatic beam and ease of fabrication into one or two dimensional arrays.
For many of these applications, a single mode output is required from the VCSEL. However, VCSELs tend to have poor spatial mode discrimination and nonuniform current injection. One of the challenges in the current state of VCSEL technology is the achievement of higher levels of output power with single mode behavior.
One means to achieve a single mode VCSEL is to reduce the reflectivity for the higher order modes within the laser aperture.
It is an object of the present invention to provide a vertical cavity surface emitting laser operating in a single mode.